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Chapter 1

What are crystals?

Everybody has heard of crystals. The word "Crystal" is used in

reference to a type of jewel which has a healing, spiritual or

decorative objective. Therefore, according to how the word is used,

one can assume that crystals can be used for different purposes.

But what are crystals really?

Crystals are minerals which solidify as a result of a natural

geological and chemical process. They have a unique and specific

chemical composition. They also possess extremely well-ordered

atoms and specific physical properties which are distinct for each

particular kind of crystal. Even if people call them "pretty stones",

their composition is in fact quite specific, as opposed to a

gemstone which is an agate made of minerals and/or mineraloids

(substances that have no crystallinity) but which does not have a

specific composition. The composition of a mineral can range from

pure elements of simple salts to complex silicates with thousands

of different shapes. The study of minerals is known as mineralogy.

So a crystal, in simple terms, is a mineral.

For a mineral to be classified as a "true mineral", it must have a

crystalline structure and a solid form. It must also have a

homogeneous substance which occurs naturally with a defined

chemical structure. A "crystal" possesses a geometrical spatial

arrangement of atoms within its structure. There are 14 different

three-dimensional structural arrangements of atoms known as the

"Bravais Lattice". Each of these structures can be classified in one

of the seven systems of crystals. All recognized crystals to date are

divided into one of the Bravais Lattices within one of the seven

systems.Certain gemstones are all mineral, such as limestone, which is

basically a sedimentary rock made completely of crystallised

calcium carbonate. The stones that constitute the earth's crust are

composed of quartz, feldspar, mica, chlorite, kaolin, calcite,

epidote, olivine, augite, hornblende, magnetite, hematite, limonite

and a few other minerals.

Some minerals can be commonly found all over the world, while

others are only located in specific places. More than half of the

known minerals are so rare that only a handful of samples have

been discovered and many are known thanks to one or two little

grains. Classifying minerals can range to very simple to extremely

complex. A mineral can be classified and identified by several

physical properties. Others have been identified thanks to

techniques such as X-rays. According to the International

Association of Mineralogy, which is responsible for the approval

and naming of newly discovered minerals, there are currently 4,000

known minerals. Among these, perhaps 100 could be called

"common", 50 "infrequent" and all the rest "rare" to "extremely rare